The present invention relates to electric energy meters, and more particularly to a method and apparatus for mounting the disk sensing optics on the register printed circuit board of a time of use electric energy register.
The use of electronics in electric energy meters has enabled the design of energy meters with greatly increased capability and functions. However, there is increasing pressure for such meters to have fewer parts and to be substantially smaller than previous designs. Fewer parts are required in order to minimize manufacturing costs, including the cost of materials and assembly, and the subsequent cost and number of components which must be maintained for spare parts and repair purposes, along with an increase in reliability which accompanies designs which have fewer parts.
Induction watthour meters conventionally utilize the rotation of an eddy current disk in response to the power consumption on the lines being metered, which is then totalized or integrated as a measure of energy consumption, usually in Kilowatt hours. In electronic registers for use in induction watthour meters, a series of electrical pulses is used to provide an electrical signal responsive to the rate of energy consumption. This is usually achieved by mounting a toothed optical shutter on the eddy current disk shaft of the meter for rotation with the shaft, and positioning a light source and detector on opposite sides of the shutter. The toothed shutter interrupts the light path between the light source and a light detector as it rotates between them at a rate proportional to the rate of energy consumption by the load being metered. Two pairs of light emitters and detectors are typically used in such arrangements in order to detect shutter rotation direction. Typically, the light emitting and detecting pairs are housed in an assembly separate from the register and interconnected to the register by means of a cable. Directly mounting the disk sensing optics on the register printed circuit board eliminates the need for a separate circuit board and connecting cable, and in addition assists in reducing the size of the electronic register along with a reduction in other parts. However, the components of the disk sensing optics have to be accurately located relative to each other and to the optical shutter, and in addition must be shielded from external or ambient light in an energy meter including the usual transparent housing or case which may be positioned in direct sunlight or other bright light. In addition, it is desired to obtain accurate positioning, and shielding, of the disk sensing optics while at the same time avoiding any requirement for special fixturing during the manufacturing process.